The present invention relates to a solenoid-type electromagnet for operating frequencies in the order of magnitude of about 3000 cps and higher, and more particularly, but not exclusively, the invention relates to a solenoid drive for print needles or styli in matrix printers, wherein the needles or styli or actuating elements for the needles or styli are fastened, respectively, to an axially movable armature.
Solenoid type electromagnets and drive magnets to which the invention pertains usually include some form of attenuation structure in order to reduce any shock effect such as any sudden stoppage of the magnet may entail. Solenoid magnets of this type are often used, generally, in electrical engineering and may include structure for driving various kinds of equipment such as switches, circuit brakers, etc. Such solenoid magnets are, therefore, often used in electric circuits generally as actuators for purposes of changing the state of connection within a particular circuit or for the transmission of a signal or the like. As stated above, the electromagnets of this type are particularly used in matrix printers, particularly matrix line printers, but also in so-called serial matrix print heads.
German printed patent application No. 18 06 245 discloses a solenoid type electromagnet with the principle task to obtain a high operating and switching frequency at lowest possible weight of the movable elements; the magnet or armature as such is to be of light weight; or generally the parts that are actually subject to high speed movement, particularly high speed acceleration and deceleration should be as light as possible. In addition, the attraction forces have to be adequately high. The known solution to this problem, i.e. the known solution towards providing an electromagnet for high switching and operating frequencies, is to be obtained through minimal outer dimensions as far as the respective magnet is concerned, and by combining that feature it with an optimized force-mass-ratio. This way, an attempt was made, to indeed, provide a specific solution to the problem in so-called mosaic printers. The specific solution to the problem found in that reference is then a particular construction of the movable armature.
The various aspects taken into consideration in this publication, however, fail to realize that in the case of high switching and operating frequencies, the armature often has to be stopped in an extreme short period of time so that the new current pulse can be built up. This stopping of the armature toward the end, for example, of a retraction stroke, requires particular attenuation structure. Rebounding cannot be tolerated at a time when a new energization of the magnet may commence-